This invention relates generally to an improved retrievable anchor assembly for use in well bores and the like. More particularly, but not by way of limitation, this invention relates to an improved slip and improved slip assembly for a well tool such as a retrievable anchor assembly.
Tubing anchor/catchers are, among other things,utilized in wells which have to be pumped order to produce the oil therefrom. The well bores are usually lined by casing and may have production tubing therein through which sucker rods from a reciprocating pump pass. The oil pump itself is generally suspended from the lower end of the sucker rods deep in the well.
In some well, the depths from which oil will be produced is substantial and therefore, a substantial amount of tension is exerted on the sucker rods during pumping. In fact, the upward stroke of the pump jack places tension in the rod and compression in the tubing and lowering of the rod into the tubing for the next stroke causes a force reversal, that is, a compressive force to be exerted on the rod and a tension force on the tubing. It has been calculated that in an unanchored tubing string being pumped at the rate of 15 strokes per minute, the destructive tubing movement occurs 21,600 times a day on each upstroke. Such buckling of the tubing during the pump stroke causes substantial friction drag and thereby increases the surface power requirements. Also, the reversal of forces occurs 21,600 times each day causing the couplings of the tubing to rub against the casing with resulting coupling wear.
From the foregoing, it will be appreciated that a reversal of forces with their attendant increased friction, wear, and increased power requirements occurs approximately one million times each month. The result of such force reversal is the mechanical erosion of metal from the rods, from the tubing inside diameter and from the exterior of the couplings. Production losses and increased costs occur from leaks in the tubing, higher power requirements, and from more down time necesssitated by the replacement of the broken rods and leaking tubing. The use of an effective tubing anchor eliminates many of these problems.
The devices which lock the anchor in the casing are known as slips in the industry. Slips or grippling slips, as they are sometimes called, come in many shapes and various locking configurations. Essentially all slips have exterior teeth and a tapered inner surface that reacts with a tapered expander surface to force the slip teeth into holding engagement with the casing.
Retrievable anchor assemblies of the general type involved in this invention have been constructed and sold by Brown/Hughes under the designation Brown Type M-2, Arrow Oil Tools, Inc. under the designation Arrow Type R Tubing Anchor Catcher, sold by Baker Service Tools under the designations Models B-2 and B-3, as well as by the Guiberson Division of Dresser Industries, Inc., the assignee of this application, under the designation Type TM Tubing Anchor-Catcher.
Each of the foregoing described tools has provided to be reasonably reliable for their intended purpose. However, it is believed that the aforementioned tools were designed at a time when the oil industry was prosperous and accordingly, the tools are comparatively heavy, expensive and in some cases complex beyond that necessary to perform the tubing anchor function properly.
It is an object of this invention to provide an improved slip and slip assembly for retrievable anchors that provides all of the advantages of the prior art devices while at the same time providing an efficient and securely holding anchor utilizing a slip assembly that is effective, easily assembled in the anchor, easily maintained and that can be produced less expensively than comparable slip assemblies.